Apparatus for developing a powder image on a xerographic plate



Jan. 15, 1957 R. w. GUNDLACH 2,777,418

APPARATUS FOR DEVELOPING A POWDER IMAGE ON A XEROGRAPHIC PLATE 11V VENTOR. ROBERT W. GUNDLACH ATTORNEY Jan. 15, 1957 R. w. GUNDLACH APPARATUSFOR DEVELOPING A POWDER IMAGE ON A XEROGRAPHIC PLATE Filed Feb. 8, 1954I 4 Sheets-Sheet 2 FIG. IO

INVEN TOR. ROBERT W. GUNDLACH I M ATVTORN E1 Jan. 15, 1957 R. w.GUNDLACH 5 APPARATUS FOR DEVELOPING A POWDER IMAGE ON A XEROGRAPHICPLATE Filed Feb. 8, 1954 4 Sheets-Sheet s FIGB JNVENTOR. ROBERT WGUNDLACH AT'ITORNEY Jan. 15, 1957 R. w. GUNDLACH 297779418 APPARATUS FORDEVELOPING A POWDER IMAGE ON A XEROGRAPHIC PLATE Filed Feb. 8, 1954 4Sheets-Sheet 4 l8 8 FIG.4 |a

INVENTOR. ROBERTWGUNDLACH United States Patent APPARATUS FOR DEVELOPING-A.-rownnn IMAGE ON A XEROGR'APHIC PLATE Robert W. Gundlach,Spencerport, N; Y., as'sig'nort'o The Haloid Company, Rochester, N. Y.,a corporation of New York This invention relates to a method andapparatusfor developing a powder'image' on a xerographicplate and hasfor its primary purpose to improve the character of xerographic copiesby producing more uniformity and greater blackness or darkness in theimage areas and by preventing to a greater extent than heretofore theadherence of developer powder to the non-image or discharged areas.

In the production of xercgraphic copies, the usual procedure is first tocharge electrostatically the photo conductive insulating image layer ofa xerographicplate, then expose the charged surface of the image layerunder light to the subject to be copiedproducing an electrostatic image,after which the image layer with the electrostatic image thereon issubjected to the cascading operation of electroscopic or developerpowder thereove-r to produce a powder image which is thereaftertransferred and affixed to paper or other transfer medium, and theprocedures as heretofore practiced have resulted in the image areas ofthe copy being black or darkadiacent to their edges and light or whiteat the central areasowing to the improper and non-uniform adherence ofdeveloper powder to the image areas, and it is a purpo'seof theinvention to overcome this difficulty by bringing about uniformadherence of the developer powder over the entire image areas, therebyproducing uniformly black or dark image areas in the finished copy.

in the development of powder images on flat xerogr'aphic plates, afurther difliculty has been experienced in effectively removing all ofthe developer power from the discharged or background areas where theelectrostatic charge has been conducted olfu'pon exposure of thexerographic plate, and afurther purpose is toenable an effective andmore completeremoval of developer powder from the discharged orbackground areas, in addi tion to more uniform adherence ofthe'developer powder over the image areas when developingflat'xerographic plates.

The invention further resides in the provision'of a practical andefiicient apparatus for carrying out the above stated purposes by theapplication to a powder cascading receptacle of a development electrodesuitably'retained in the receptacle and including aconductingplatepositioned in close proximity to the image layerandprovided with electrical charging means operative to impose apotential on the conductingflplate and produce afield between thexerographic plate and the development electrode, the conducting platebeing positioned and arranged toes'tabli'sh contact through'a batterycircuit withthe-metalliobtrcking of a xerographic plate located inthepowder receptacle, thus establishing connection from the metallicbacking of the xerogr'aphic plate to the current source that imposes thecharge on the development electrode.

To these and other ends, the invention consists in the construction andarrangement of parts that will appear clearly from the followingdescription when read in con junction with the accompanying drawings,thenovel fea- 2,777,418 Patented Jan. 15, 1957 tures being; pointed outin the claims following the specification.

In the drawings:

Fig. 11 is a perspective view looking toward the inner surface of thedevelopment electrode, the latter being removed. from thepowderreceptacle;

Fig. -2 is a longitudinal sectional view taken centrally through thepowder receptacle, showing the development clectrodeipartially inelevation and a xerographic plate bot-h positioned in the powderreceptacle, and the latter arranged to cascade developer powder over thecharged image layer of the xerographic plate;

Fig. 3 is a perspective view of the powder receptacle with thedevelopment electrode removed;

Fig 4 is a transverse sectional view of the development electrode;

Fig. 5 is a transverse sectional view of the powder receptacle;

Fig. 6 is a view similar to Fig. 5-, showing the initial position of thedevelopment electrode while being inserted into the powder receptacle;

Fig. 7 is a view similar to Fig. 6, illustrating an intermediateposition of the development electrode while being inserted into thepowder receptacle;

Fig. 8 is a view similar to Fig. 7, illustrating the final position ofthe development electrode when yieldably supported in the powderreceptacle;

Fig. 9 is a sectional view taken transversely of Fig. 2, illustratingthe relationship between the contact shoes of the development electrodeand the metal backing or support of the xerographic plate, whenpositioned in the powder receptacle, and

Fig. 10 is a diagrammatic view of the circuit connecting the batterymeans of the development electrode with the metal backing of thexerographic plate.

Referring more particularly to the drawings in which like referencenumerals refer to the same parts throughout the several views and whichare intended to serve only as an example of one practical embodiment ofthe invention, there is illustrated a powder receptacle, see Figs. 2, 3,and 5 to 8 inclusive, of the general character illustrated in Patent No.2,600,580, dated June 17, 1952, and including a bottom wall 1 and a topwall having an opening therein defined by lateral flanges 2 extendingaround the opening and supporting compressible or rubber strips 3 and 4against which the xerographic plate 5 is held by spring catches 6 whenpositioned in the powder receptacle, see Fig. 2.

The powder receptacle with the xerographic plate held therein isoscillated to cascade the electroscopic or developer powder alternatelyin opposite directions over the xerographic plate in a manner similar tothat disclosed in the aforementioned Patent No. 2,600,580, and thestructure thus far described is susbtantially in accordance with suchprior patent while the present invention has to do more particularlywith a development electrode that is arranged within the powderreceptacle and includes a conducting plate located parallel and inslightly spaced relation to the image surface of the xerographic platewhile cascading the developer powder over the image surface of thexerographic plate, the powder moving between the image surface and thedevelopment electrode plate which is arranged in close proximity to thexerographic plate during the powder developing operation.

To accomplish this, the powder receptacle is provided with metal springs7 suitably attached to the bottom wall 1 of the powder receptacle andhaving upwardly extending free ends upon which the development electrodeis yieldably supported when located in operative position in the powderreceptacle. The development electrode, which is illustrated in detail inFig. 1, includes a conducting or 3 metal plate 3 that terminates at itsends in flanges 9 extending inwardly, see Figs. 1 and 2, which functionto deflect the developer powder indicated at 11, Fig. 2, to between theconducting plate 8 and the xerographic plateand to prevent the main bodyof developer powder from passing to the central area of the powderreceptacle above the development electrode during the powder cascadingoperation.

The development electrode also includes a battery case 12 attached tothe plate 8 and housing preferably three 30-volt batteries 13 connectedin series and all protected by a cover plate 14. The battery at one endis connected to the conductor plate 8 while the battery at the oppositeend of the battery case is connected through a suitable resistor 15 toconducting strips 16 mounted on the metal shoes 17 which are insulatedfrom the conducting plate 8 by blocks of insulating material 18, while19 indicates supporting lugs at the ends of the shoes 17 arranged toengage the portion of the grounded metallic or aluminum conductingbacking 21 of the Xerographic plate surrounding the selenium orphoto-conductive image layer 22 when in position to receive thedeveloper powder. The lugs 19 of the shoes act to hold the conductingplate 8 and xerographic plate 5 spaced from each other preferably adistance of approximately and the conducting strips 16 afford aconnection from the metal backing of the xerographic plate to thebattery and conducting plate 8, producing an electrostatic field betweenthe conducting plate 8 and the image layer of the xerographic plate whenthe parts are in position for developing. I The development electrodeisremovably held within the powder receptacle by legs or extensions 23on the shoes 17, the legs 23 engaging under the flanges 2 of the powderreceptacle when operatively positioned therein. The developmentelectrode is positionable within the powder receptacle by inserting itfrom one side, see Fig. 6, depressing the adjacent ends of springs 7thereunder until legs 23 at the opposite side of the developmentelectrode can be brought under the flange 2 as illustrated in Figs. 7and 8, and when the development electrode is finally positioned, thesprings 7 serve to hold it yieldably through the action of the springs7, see Fig. 8, while the legs 23 limit the outward movement of thedevelopment electrode and retain it against outward movement beyond theflange 2. When the xerographic plate is secured in position as in Fig.2, the lugs 19 engage the metal area around the image layer of thexerographic plate and are held thereagainst by the yielding action ofsprings 7, the xerographic plate being held against the developmentelectrode by the spring catches 6 previously mentioned, and under whichthe xerographic plate is inserted when positioned in the powderreceptacle.

The structure is such that when the xerographic plate is operativelypositioned for developing, its image surface isapproximately from thesurface of the conducting plate 8, which has a uniformly flat andunbroken surface throughout its area with an error of uniformity of notmore than i a. The spacing between the conducting plate 8 and the imagelayer of the xerographic plate is preferably not more than suflicient topermit movement of the developer powder over the image layer and enablethe developer powder to adhere to the charged image areas.

The Xerographic plate when charged usually has a potential ofapproximately 600 volts while after exposure, a charge of approximately10 to 30 volt potential remains on the background or discharged areaswith the full charge vcentrated image with lines that are not diffused,as contrasted with powder developing procedures in which there is noconducting plate in parallel relation and close proximity to thexerographic plate and in which the lines of force from the edges orouter portions of an image area are consequently directed in curvedpaths to the adjacent discharged or background areas, resulting in thelines of force being dissipated from the image area and producing blackor dark efiects around the edges and light or white effects at thecentral portions.

The potential imposed on conducting plate 8 of the development electrodeis preferably from 60 volts to 90 volts, with a polarity the same as thepolarity of the charged image areas and the same as the polarity of thecharge on the background areas of the xerographic plate but with agreater voltage than that of the charge on the background areas,resulting in an electrical field which neutralizes the field caused bythe residual charge on the discharged or background areas. In thismanner, the conducting plate 8 prevents developer powder from adheringto the discharged or background areas, and produces a copy havinguniformity in both the image and background areas, with more perfectcontrast between the image and background areas, and greatly improvedquality of the copy.

For the purpose of uniform development of the image areas, theconducting plate 3 of the development electrode may be maintained atground or substantially zero potential, and the potential which isimposed on the conducting plate 8 for preventing adherence of powder tothe discharged or background areas is comparable to the residual voltageon the discharged areas, while the maximum potential on the conductingplate 8 is sufficiently low so as not to affect the powder on the imageareas.

While the invention has been disclosed with reference to the particularstructure herein shown, it is not confined to the details andarrangement set forth, and this application is intended to cover suchmodifications or departures as may come within the purposes of theimprovement or the scope of the following claims.

I claim:

1. A portable apparatus for developing a powder image by gravitatingdeveloper powder over the insulating image remaining on the undischargedor image areas, and the conducting plate 3 of the development electrodecauses the lines of force from the undischarged or image areas to bedirected in generally parallel relationship toward the conducting plate8 in perpendicular relationship to the image surface and to theconducting plate 8. This results in uniform adherence of the developerpowder over the image area and produces a uniformly dark or con]-surface of a flat Xerographic plate having a conductive metal backing,which consists of a powder receptacle adapted to be manually oscillatedto gravitate the developer powder over the surface of said plate, meansfor supporting the Xerographic plate in the powder receptacle, 2.development electrode consisting of a uniformly flat conducting platethat is uniformly spaced from said image surface a distance ofapproximately means for removably supporting the development electrodeabove the i plate-in the powder receptacle, and electric charging meansconnected to said conductive backing and to said development electrodeand operating to impose on said development electrode a charge having apotential of from 60 volts to volts, said potential being greater thanthe potential of the background areas of the image on the plate and lessthan the potential of the image areas and acting to prevent adherence ofdeveloper powder to the background areas and to effect uniform adherenceof the developer powder to the image areas and thereby producinguniformly black image areas.

2. A portable apparatus for developing a powder image by gravitatingdeveloper powder over the insulating image surface of a flat Xerographicplate having a conductive metal backing, which consists of a powderreceptacle adapted to be manually oscillated to gravitate the developerpowder over the surface of said plate, means for supporting thexerographic plate in the powder receptacle, yieldable supporting meansin said powder receptacle, a development electrode removably mounted onsaid yieldable supporting means above the plate, flanges in the powderreceptacle against which said development electrode is yieldably held,the development electrode being spaced uniformly from the insulatingimage surface a distance of approximately 7 said development electrodeconsisting of a uniformly flat conducting plate, a battery attached toand insulated from the under surface of said conducting plate, saidbattery connected at one end to said conducting plate, conducting shoescarried by and insulated from said conducting plate and connected to theother end of said battery, lugs carried by said conducting shoesextending inwardly therefrom and engaging the metal backing of theXerographic plate, and extensions on said shoes engaging the aforesaidflanges and holding the electrode above the plate in the powderreceptacle, said conducting shoes and lugs acting as conductors betweenthe battery and the metal backing of the xerographic plate and thebattery having a capacity and acting to impose on said conducting platea charge having a potential of from 60 volts to 90 volts, said potentialbeing greater than the potential of the background areas of the image onthe plate and less than the potential of the image areas and acting toprevent adherence of developer powder to the background areas and toeffect uniform adherence of developer powder to the image areas andthereby produce uniformly black image areas.

References Cited in the file of this patent UNITED STATES PATENTS1,932,057 Wheeler Oct. 24, 1933 2,173,078 Meston Sept. 12, 19392,233,037 Smith Feb. 25, 1941 2,381,455 Jacob Aug. 7, 1945 2,551,582Carlson May 8, 1951 2,558,900 Hooper July 3, 1951 2,573,881 Walkup eta1. Nov. 6, 1951 2,633,796 Pethick Apr. 7, 1953 2,725,304 Landrigan etal Nov. 29, 1955 FOREIGN PATENTS 188,030 Great Britain Oct. 23, 1922698,994 Great Britain Oct. 28, 1953

